1. Field of the Invention
The invention relates to fire- and heat-resistant bisimide resins obtained by thermal polymerization of maleimido or citraconimido derivatives of 1-[(diorganooxyphosphonyl)methyl]-2,4- and -2,6- diaminobenzenes.
2. Description of the Art
High temperature resistant polymers are used extensively in advanced aerospace structures in which structural integrity must be retained during continuous use at temperatures of 325.degree. C. and above. The stringent requirements of space technology and of other industrial applications for thermal protective materials have led to the development of several classes of heat- and fire-resistant heterocyclic polymers. Aromatic polyimides have met these requirements to a large extent and are obtained by condensation reactions. However, the loss of desirable mechanical properties and problems of reproducibility have been observed because of the voids created by the elimination of water or difficulty in the removal of the high-boiling-point solvent or both. As a result, the use of these polyimides as laminating resins or for adhesives has been limited.
Initial attempts to overcome these processability problems led to the development of addition polyimides based on short, preimidized segments which polymerize thermally through end groups without loss of volatiles. However, these polymers were found to be inherently brittle because of the extensive cross-linking which occurs during polymerization. Several amine-capped liquid elastomeric prepolymers reacted with bismaleimides to produce polymers. See for example, P. Kovacic, U.S. Pat. No. 2,818,405; Chem. Abstracts, 52, 5018e (1958). However, these polymers could not be considered heat-resistant.
Several investigations concerning flame retardation of polyimide resins prepared from phosphorous-containing prepolymers, end-capped with reactive maleimido rings, have been recently reported. Bisimide resins based on bis(m-aminophenyl)methylphosphine oxide as well as bisimide and triimide resins based on tris(m-aminophenyl)phosphine oxide have been prepared and tested as a matrix for fiber-reinforced composites. See, for example, U.S. Pat. No. 4,276,344 and I. K. Varma, G. M. Fohlen and J. A. Parker, J. Macromol.Sci-Chem, (1), 39 ff (1983). Some of the polymer precursors show a relatively high curing temperature or yield inherently brittle polymers due to their high cross-linking density. It is desirable to have organic matrix resins with a low curing temperature so as to obtain polymers with reduced brittleness.
Some patents of general interest in this field include the following U.S. Pat. Nos. 3,929,713; 4,269,961; 4,107,153; 4,276,344; 4,283,522; and 4,421,820.
Some references of the inventors, which describe fire resistant compositions of phosphorus-containing polymers and the monomers thereof, include the following:
1. J. A. Mikroyannidis and D. A. Kourtides, "Fire-Resistant Compositions of Epoxy Resins with Phosphorus Compounds", Symposium on Rubber-Modified Thermoset Resins, 186th Annual American Chemical Society Meeting, Washington, D.C., Abstract PMSE 133, Aug. 28 - Sept. 2, 1983;
2. J. A. Mikroyannidis and D. A. Kourtides, "Fire-Resistant Epoxy Resins Containing 1-(Di(2-Chloroethoxy phosphinyl) Methyl)-2,4- and 2,6 Diaminobenzene as Curing Agent", Proceedings of the 12th North American Thermal Analysis Society Conference, Williamsburg, Va. (Sept. 1983);
3. J. A. Mikroyannidis and D. A. Kourtides, "Curing of Epoxy Resins with 1-[Di(2-Chloroethoxyphosphinyl)Methyl]-2,4- and 2,6-Diaminobenzene", Journal of Applied Polymer Science, Vol. 29, pp. 197-209, (1984);
4. J. A. Mikroyannidis and D. A. Kourtides, "Curing of Epoxy Resins with 1-[Di(2-Chloroethoxyphosphinyl)Methyl]-2,4- and 2,6-Diaminobenzene", National Aeronautics and Space Administration Report No. TM 84350, October 1983;
5. J. A. Mikroyannidis and D. A. Kourtides, "Synthesis and Characterization of Phosphorus-Containing Polyamides and Copolyamides based on 1-[Dialkoxyphosphinyl)Methyl]-2,4- and -2,6-Diaminobenzenes", Journal of Applied Polymer Science, Vol. 29, pp. 941-953 (1984);
6. J. A. Mikroyannidis and D. A. Kourtides, "Synthesis and Characterization of Phosphorus Containing Polyamides and Copolyamides Based on 1-[(Dialkoxyphosphinyl) Methyl]-2,4- and -2,6-Diaminobenzenes", Proceedings of the Society for the Advancement of Materials and Process Engineering, Reno, Nev. (April 1984); and
7. J. A. Mikroyannidis and D. A. Kourtides, "Curing of Epoxy Resins with 1-[Di(2-Chloroethoxyphosphinyl)Methyl]-2,4- and -2,6-Diaminobenzene", Proceedings of the Society of Plastics Industry Annual Spring Meeting, St. Louis, Mo. (May 1984).
These references of the inventors are not considered to be prior art concerning the present invention.